1. Field of the Invention
The present invention relates to an optical disk reproducing system such as a compact disk player (CDP) and a digital video disk or a digital versatile disk (DVD) player, and more particularly, to a data restoring apparatus in an optical disk reproducing system for restoring data recorded on an optical disk from a radio frequency (RF) signal read from the optical disk.
2. Description of the Related Art
In an optical disk reproducing system, a pick-up circuit includes a photodiode which senses light transmitted to a disk, and reflected from the disk according to the presence of pits on the disk, and converts the sensed, reflected optical signal into an analog RF signal according to whether the voltage of the RF signal is higher or lower than a reference voltage (Vref). The decoded data stream is eight-to-fourteen modulation (EFM) demodulated and is restored to effective 8-bit data.
In such an optical disk reproducing system, the data is classified according to the lengths of the pits on the surface of the disk. However, for a rotating disk, the effective pit lengths vary with disk rotation speed. For example, a faster rotation speed causes the pits to appear shorter in length. To address this issue, a recovery clock signal used for restoring EFM data from an RF signal is locked to the RF signal. Namely, it is possible to restore correct data since the frequency and phase of the recovery clock signal are locked to those of the RF signal even for a time period where the disk rotates at a variable or non-constant speed. A phase locked loop (PLL) is used for locking the frequency and phase of the recovery clock signal to those of the RF signal. In conventional technology, an analog PLL is primarily used.
In the case of a CDP, the recovery clock signal (or a channel bit clock signal) is at a frequency of 4.3218 MHz. In the case of a DVD, the recovery clock signal is 26.16 MHz. In each case, it is possible to obtain a desired data stream when the recovery clock signal is locked to the RF signal when data is reproduced at 1xc3x97 speed. However, as the data transmission rate becomes higher and when the method of controlling the rotation speed of the disk changes from a constant linear velocity (CLV) to a constant angular velocity (CAV), it is necessary to more finely control the frequency and phase of the recovery clock signal. Also, when the conventional PLL is used, the frequency of the recovery clock signal becomes unstable during the control of the phase since the phase of the recovery clock signal is controlled not by fixing the frequency but by locking the phase by instantaneously changing the frequency.
With recent increasing rotation speeds, the data restoring ability according to the rotation speed of the disk and the data restoring ability by the instability and the distortion factor of the RF signal become the primary variables that affect the performance of the optical disk reproducing system. It is desired that data recorded on disks of various speeds can be correctly restored by a single optical disk reproducing system. Although the RF signal can be unstable due to frequency and phase error or due to a cumulatively-added error value, correct data should be restored by compensating for the instability of the RF signal. However, according to the conventional analog method, filters having cut-off frequencies corresponding to the respective speeds and circuits for controlling the filters are required. Also, in the analog system, data can be lost since it is impossible to variably restore data corresponding to the variety of types of optical disks, the differences between processes of manufacturing the optical disks, and the instability of the optical disk used a recording medium. In particular, as higher-speed transmission and higher data density are required, data-restoring performance deteriorates due to the interference between signals when data is restored according to the analog method.
To address the above limitations, it is an object of the present invention to provide an apparatus for restoring data in an optical disk reproducing system by which it is possible to restore correct data by digitally calculating frequency and a phase error between a recovery clock signal and an RF signal and compensating for the frequency and a phase error.
It is another object of the present invention to provide an apparatus for restoring data of an optical disk reproducing system by which it is possible to restore correct data by digitally compensating for the asymmetry in the RF signal.
It is still another object of the present invention to provide an apparatus for digitally and correctly compensating for the asymmetry of an analog signal.
Accordingly, to achieve the first object, there is provided a data restoring apparatus in an optical disk reproducing system for restoring data recorded on an optical disk from an RF signal read from the optical disk, comprising an analog to digital converter (ADC) for digitally converting the RF signal in response to a recovery clock signal and generating the digitally converted signal as a digital RF signal, a decoder for decoding the digital RF signal and generating a decoded bit stream as restored data, an adaptive phase error compensator for obtaining the phase error between the RF signal and the recovery clock signal and for generating a control voltage corresponding to the phase error, and a voltage controlled oscillator for generating the phase compensated recovery clock signal by varying the frequency of the recovery clock signal according to the control voltage, wherein the adaptive phase error compensator adds a predetermined number of successive digital RF signals generated around a reference voltage and obtains the sum as the phase error.
To achieve the first object, a data restoring apparatus of an optical disk reproducing system for restoring data recorded on an optical disk from an RF signal read from the optical disk preferably comprises an analog-to-digital converter (ADC) for digitally converting the RF signal in response to a recovery clock signal and generating the converted signal as a digital RF signal, an edge detector for detecting an edge at which the digital RF signal crosses the reference voltage, and generating the detected edge as an edge detection signal, a frequency error compensator for detecting the frequency error between the digital RF signal and the recovery clock signal, generating a control voltage for compensating for the frequency of the recovery clock signal according to the detected frequency error, and locking the control voltage when the frequency of the recovery clock signal is locked to that of the digital RF signal, a phase error compensator for obtaining a phase error indicating whether the phase of the recovery clock signal lags or leads that of the RF signal, and a viterbi decoder for decoding the phase compensated digital RF signal generated by the phase error compensator with a viterbi decoding method and generating the decoded bit stream as restored data.
To achieve the first object, a data restoring apparatus of an optical disk reproducing system for restoring data recorded on the optical disk from the RF signal read from the optical disk comprises an analog-to-digital converter for digitally converting the RF signal in response to the recovery clock signal and generating the converted signal as a digital RF signal, an edge detector for receiving the digital RF signal, detecting an edge at which the digital RF signal crosses the reference voltage, a frequency error compensator for obtaining a maximum coefficient value by cumulatively adding a predetermined value K or the digital RF signal according to the edge detection signal during the duration of the maxim duty signal (14T or 11T) in the RF signal in a period of the predetermined term, a phase error compensator for obtaining a phase error according to whether the phase of the recovery clock signal lags or leads that of the RF signal and generating the phase compensated digital RF signal, and a viterbi decoder for decoding the phase-compensated digital RF signal generated by the phase error compensator by a viterbi decoding method and generating the decoded bit stream as restored data.
To achieve the second object, there is provided a data restoring apparatus of an optical disk reproducing system for restoring data recorded on the optical disk from the RF signal read from the optical disk, comprising an analog-to-digital converter (ADC) for digitally converting the RF signal in response to a recovery clock signal, an adder for adding a reference voltage compensation value to the signal generated by the ADC and generating the addition result as a digital RF signal, a reference voltage for obtaining a cumulatively added error value by adding a predetermined number of digital RF signals successively generated around a reference voltage and generating a reference voltage compensation value according to the obtained cumulatively added error value, and a viterbi decoder for decoding the digital RF signal by a viterbi decoding method and generating the decoded bit stream as restored data.
To achieve the second object, a data restoring apparatus of an optical disk reproducing system for restoring data recorded on the optical disk from the RF signal read from the optical disk preferably comprises an analog-to-digital converter for digitally converting the RF signal in response to a recovery clock signal and generating the digitally converted signal, a digital sum value (DSV) controlling portion for receiving the digitally converted signal and generating a voltage compensation value so that the number of signals having levels higher than a reference voltage is equal to the number of signals having levels lower than the reference voltage, an adder for adding the voltage compensation value to the signal generated by the analog-to-digital converter and generating the addition result as a digital RF signal, and a viterbi decoder for decoding the digital RF signal by a viterbi decoding method and generating the decoded bit stream as restored data.
To achieve the third object, there is provided an apparatus for compensating for the asymmetry of a received analog signal, comprising an analog to digital converter for digitally converting the analog signal in response to a recovery clock signal, an adder for adding a reference voltage compensation value to the signal generated by the ADC and generating the addition result as a digital signal, and a reference voltage for obtaining a cumulatively added error value by adding a predetermined number of successive digital signals around the reference voltage when the digital signal approaches the reference voltage and generating the reference voltage compensation value according to the obtained cumulatively added error value.
To achieve the third object, an apparatus for compensating for the asymmetry of a received analog signal preferably comprises an analog-to-digital converter for digitally converting the analog signal in response to a recovery clock signal, a DSV controller for receiving a digital signal generated by the ADC and generating a voltage compensation value so that the number of signals having levels larger than a reference voltage is equal to the number of signals having levels smaller than the reference voltage, and an adder for adding the voltage compensation value to the signal generated by the ADC and generating the addition result as a digital signal whose asymmetry is compensated for.